Various roofing structures and systems are known. The object of most roofing systems is to provide insulation for the building which the roof covers, to keep the building dry, and yet to prevent water vapor from accumulating within the roofing system or structure. Accumulation of water vapor is damaging or destructive to the roofing system. Yet it is difficult to keep water out of the building and at the same time to prevent build-up of water vapor within the roofing structure. In addition, the roofing systems must be strong enough to support any wind load and snow loads to which it is subjected, to permit a person to walk on the roof, and (where desired) support an aesthetically pleasing exterior member which constitutes the top layer of the roofing structure. Existing roofing systems achieve the aforesaid objects with varying degrees of success. In some cases there is a tradeoff in which performance in one area is sacrificed in order to achieve top performance in another area. In particular, it is difficult to keep a building dry and at the same time to prevent the build-up of water vapor within the roofing structure. Various constructions have been proposed in order to achieve both objects.
Applicant's U.S. Pat. No. 4,804,578 discloses an insulated roof board comprising a base layer of rigid coherent insulating material, an intermediate layer comprising a plurality of small shaped bodies, preferably polystyrene beads, which are adhesively joined together and which provide void space for lateral venting of water vapor, and a relatively hard, dense top layer. The base layer is preferably made of a foam plastic insulating material such as polystyrene. The hard dense top layer is a protective layer preferably made of a coherent cellulosic material such as fiber board or hard board. Also shown is a roofing assembly which incorporates the aforesaid insulated roof board. While the insulated roof board shown therein is light in weight, strong, and highly effective in venting water vapor, it is comparatively expensive to manufacture because of the cost associated with forming the intermediate layer, which requires adhesively securing to each other and to the base layer a large number of shaped bodies such as the aforesaid polystyrene beads.
Sterrett et al U.S. Pat. No. 3,619,961 discloses a foamed polystyrene insulation board having grooves extending in one direction along the top and bottom surfaces thereof, and at least one channel extending horizontally along an edge of the board in a direction transverse to the direction of the grooves. The channel is at an elevation intermediate between the elevations of the grooves, the top and bottom edges of the channel lying in parallel planes which are the respective planes of the troughs of the top set and the bottom set of grooves. While the channel is in communication with the grooves, communication is in the vertical direction only, i.e., across the aforesaid planes at the places of intersection. The channel and the grooves permit venting of water vapor. The polystyrene board may be situated on a suitable base member such as concrete, and on top of this board may be placed an additional insulating layer (e.g., lightweight insulating concrete) and a water impermeable (e.g., bituminous coating roofing felt) top layer.
Hyde et al U.S. Pat. No. 3,763,614 discloses a roof construction which includes a thermal insulating layer having fissures therein. A protective layer is disclosed on the top surface of the thermal insulating layer. Below this insulating layer are (in descending order) a water impermeable membrane, a second insulating layer and a metal roof deck.
Van Wagoner U.S. Pat. No. 4,021,981 discloses a roofing systems which comprises an insulation course and a protective layer, the former being placed atop of a vapor impermeable membrane. The insulation course may be made of an expanded foam, e.g., polyurethane or a polystyrene, glass beads, insulating concrete, or bituminous blocks. The protective course is a fire-retardant material which is water but not vapor impermeable. Various materials are suggested, and a fiberglass reinforced surface bonding cement containing an acrylic polymer emulsion additive is preferred.
Schuller et al U.S. Pat. No. 3,135,069 and Frohlich et al U.S. Pat. No. 4,189,886 show other roofing structures with various layers through which air and water vapor may pass.
Bellemy U.S. Pat. No. 3,598,688 shows a roofing construction which includes a waterproof layer and a resistant layer having vent openings therethrough at periodic intervals.
While various roofing constructions have been proposed, none except that shown in applicants aforementioned U.S. Pat. No. 4,804,578 has fully achieved the various desired characteristics of a roofing system, and the roof board therein (as well as other insulated roof constructions employing polystyrene beads) have relatively high manufacturing costs.